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400 BCE
Atom discovery
Democritus was a Greek philosopher who realised that everything is made up of tiny particles. He called these particles atoms from the Greek word atomos meaning indivisible. -
John Dalton
John Dalton, a British Scientist looked again at Democritus's ideas about atoms. Dalton stated that atoms were like hard balls that couldn't be split, and different atoms must have different masses -
Neils Bohr Atom
Niels Bohr adapted Ernest Rutherford's nuclear model. Bohr did calculations that led him to suggest that electrons orbit the nucleus in shells. The shells are at certain distances from the nucleus. The calculations agreed with observations from experiments. -
JJ Tompson Plum Pudding Model
When JJ Tompson carried out an experiment and, after a while, discovered the plum pudding model. This model suggests the early atom model. In the model design, there is a ball of positive charge, with smaller balls of negative charge embedded inside of it. -
Albert Einstein
Albert Einstein was able to prove that atoms actually existed. He reasoned that in order for pollen grains to move around in water they must be pushed around by atoms, otherwise how were they able to move? -
Ernest Rutherford
Ernest Rutherford proved that there were small particles inside atoms. He proved this by testing the Plum Pudding model. The experiment was that positively charged alpha particles were fired at thin gold foil. Some hit the foil however some others missed and scattered. This evidence led Rutherford to suggest a new model for the atom, called the nuclear model. In the nuclear model:
- the mass of an atom is concentrated at its centre, the nucleus
- the nucleus is positively charged -
Today
We now know that there are particles even smaller than protons, neutrons such as quarks, neutrinos, muons and gluons. Do you think there even smaller particles might be discovered in the future?
